1. Field of the Invention
The present invention relates to a lead frame having a plurality of leads, a semiconductor device made by the use of said lead frame, a lead bending die for bending the leads of the lead frame, and a method of manufacturing a semiconductor device.
2. Description of the Related Art
Many semiconductor devices have been manufactured by mounting a semiconductor chip to a lead frame, bonding the semiconductor chip to the leads of the lead frame, and then forming a package by sealing the semiconductor chip with plastic molding or the like. There are several types of semiconductor devices, classified by the arrangement of the leads (pins). Semiconductor devices are often used with leads bent substantially perpendicular to a plane of the semiconductor chip, and for this purpose, the manufacturing process includes the step of bending the leads after packaging.
Recently, electronic equipment tends to be constructed with increased packaging density, and thus it is required that individual semiconductor devices be small in size or the number of leads per semiconductor device be increased. This requires that the width of each lead and the gap between adjacent leads be narrowed. However, a problem arises if the width and the gap are narrowed, in that troubles such as undesirable deformation occurs in the leads, for example, during the bending of the leads. Accordingly, it is desired to solve this problem.
Leads of lead frames are often made by etching, thereby the width of the lead and the gap between adjacent leads are narrowed. Also, leads of lead frames are sometimes made during a punching step.
The requirements to minimize the pitch of the leads are increasing limitlessly and, recently, the width of the leads has been narrowed to such a degree that the same corresponds to the thickness of the leads. FIGS. 7A to 7C of the attached drawings show cross-sections of typical leads for illustrating that the narrow lead tends to transversely coolapse. The lead 1 shown in FIG. 7A has a width greater than the thickness thereof, and the lead 2 shown in FIG. 7B has a width substantially equal to the thickness thereof. As will be apparent, if the width of the lead is narrowed, an unstable deformation occurs in the lead. For example, the lead 1 having a large width will not tend to deform if a transverse force F is applied to the lead 1, but the lead 2 having a small width will tend to deform widthwise (transversely) if a transverse force F is applied to the lead 2; the lead 2 of FIG. 7B thus may be deformed into the shape of the lead 3 shown in FIG. 7C. Therefore, in the step of bending the leads 2 after the step of forming a semiconductor package 5, the leads 2 shift widthwise (transversely) from their predetermined bent positions, as shown in FIG. 8, and it is difficult for such a semiconductor device to be accurately mounted on a circuit board.